The present invention relates to vehicles with electronic power assisted steering.
Conventionally, the power assist for steering in vehicles is provided by a hydraulic system that is powered by the engine crankshaft. However, more recently, electronic power assisted steering (EPAS) systems have come in to use. The EPAS systems are generally lighter weight and allow for more flexibility in controlling the power assist than the conventional hydraulic systems. But the EPAS systems require significant amounts of electrical current during certain high demand steering periods (such as parking), which is generally provided by the vehicle""s alternator/battery system. Most of the time, though, a high current demand from the EPAS system is not present, and so it is also desirable to minimize the overall energy consumption that is, the current demands of the EPAS system is a high peak/low average demand. Consequently, some EPAS systems are designed with a controller that will increase the engine RPMs during these high demand periods, in order to increase the alternator output and reduce the risk of engine stall.
The drawback with these systems is that, while they employ the controller to ensure adequate current during high demand periods, it is only reactivexe2x80x94that is, it activates the necessary functions to increase the alternator output only after the high demand has already begun. Further, the inertias of the rotating components create their own time lag in assuring an adequate, timely output. So the increase in power demand remains ahead of the system response to it. When the increase in demand is faster than the system can respond, this will produce a sag in the system voltage. Furthermore, if there is a sudden reduction in demand, then a voltage spike can occur. Both the sag and spike are undesirable in that they can potentially damage vehicle electronic equipment, as well as produce undesirable vehicle operating characteristics that a vehicle operator may find objectionable.
Thus, it is desirable to have an EPAS system that overcomes the drawbacks of other EPAS systems which respond too slowly to the beginning and ending of high current demand periods from the steering system.
In its embodiments, the present invention contemplates an apparatus for a vehicle having an engine and an alternator. The apparatus includes a steering system having a steering wheel, a steering assembly operatively engaging the steering wheel and adapted to engage a vehicle wheel assembly, an electric motor operatively engaging the steering assembly, and a steering motor controller operatively engaging the electric motor. The apparatus has a steering sensor capable of determining at least one of a position of the steering assembly and a rate of movement of the steering assembly, a first determinor for determining if the steering assembly is moving toward an increase in a power requirement, a second determiner for determining an amplitude of the increase in the power requirement, and a third determiner for determining a timing of the increase. The apparatus also includes a current regulator adapted for adjusting the power output of the alternator in response to the amplitude and timing of the increase.
The present invention further contemplates a method for controlling a vehicle electric power supply that provides power to an electronic power assisted steering system. The method comprises the steps of: determining a position of a steering member; determining a rate of movement and a direction of movement for the steering member; determining if the steering member is moving toward an electrical power peak; determining the vehicle speed; calculating the derivative of the rate of movement for the steering member; calculating a first future point in time at which a particular electrical power increase is needed for the electronic power assisted steering system, if the steering member is moving toward the electrical power peak; calculating the amplitude of the particular power increase at the first future point in time, if the steering member is moving toward the electrical power peak; and adjusting the electric power supply to produce a power output that includes the particular power increase, at the first future point in time, if the steering member is moving toward the electrical power peak.
An embodiment of the present invention allows for an anticipatory control signal to be produced that can affect both the engine controller and an alternator field current regulator in order to anticipate the beginning and ending of high demand periods from the EPAS system.
An advantage of the present invention is that the alternator control loop will be better able to maintain proper vehicle system voltage during EPAS operation. In particular, voltage sags and peaks will be minimized during EPAS operation.
Another advantage of the present invention is that the vehicle driver will not experience a noticable change in intesity of, for example headlights, or lagging engine RPMs, which are both undesirable vehicle characteristics.